1973 440 Upgrade
 

Hello, I have a 73’ 440 I want to upgrade.

Engine specs :

MSD6AL / Holley Sniper EFI / Edelbrock Torker II intake / Stainless exhaust / Comp Cams camshaft : Hydraulic Flat Tappet, Advertised Duration 284/296, Lift .507/.510

Heads and pistons are stock.



I want upgrade the heads and maybe the pistons. I will go on Edelbrock Performer RPM (75cc) for stay in the RPM range of the other parts.

If I change pistons I will go on KB237, with the new head they will give me something like 10.7 comp.



My Dodge Challenger is not a race car, and I never drive it hardly, I never go above the 5000 RPM.



So, if I just change the heads, I will be at something like 9.5 comp, and I will be close to a 1970 HP 440.



So my question is : 9.5 or 10.7 comp ? What is the quality of both and the default ?

Thank you !

depends on what you want, really. i would go with 9.5 so pump gas works well and won't detonate. but if you have a nice sized wallet 10.5 is definitely gonna wake that thing up and add horses.

I think what I want is not really what I need, this engine is gold for me so I take care of it, no drag race, no big rev... My wallet is undersized, and maybe 10.7 comp will be too much for a simple build like my engine. With just the heads I will already have a big comp difference, and feel it under the right foot.

Thanks

I would not go 10.7, the oem cast pistons will do what you want and increases in compression give small percentages of power increase. My only concern would be piston to valve clearance with the new cam and likely no valve notches on piston top. Now the piston is probably far enough down the hole but I would still check it.

Thank you, I'm happy to see that change pistons is not a so good idea. I never opened the engine but I think piston are stock (the cam spec was in the trunk, I live in France and never spoke with the man who sell me the car. After google research with the name on the papers, I think the old owner is missing since 2006... So I can't ask him for piston spec...)
On papers the 1973 pistons are .123 in the hole.

The Performer RPM instructions say that : " These cylinder heads have larger-than-stock
valve sizes and may not work with the valve pockets in stock pistons, especially if a high lift cam is used. The use of aftermarket pistons and/ or custom machining to your pistons may be required."

what minimum clearance do you recommend me ?

Thanks.

The problems with not buying new pistons is two fold and the first is low compression limiting your cam choice to little more than stock. The second issue with stock 440 pistons is that they are extremely heavy ( 850 grams +-) and there cast limiting rpm to just over 5000 rpm.
I highly recommend new pistons......I've always limited the cr to 9.5 with iron heads, but I do know a few builds that are in the 10:1 cr. on pump gass with ironheads.
if your using stock heads I would stay as close to 9:1 as possible.

​​​​​​Okay thank you. The engine already have a bigger than stock camshaft (Lift .507/.510) maybe the pistons are not stock, I should check all this before buying anything. I will probably go to KB237.

My 318 has 9.2:1 stock and it had quite a bit more thump than one might think. It's great for a regularly driven street ride. If you get much higher things get dicey quick.

Okay so maybe new pistons but with a heads with more than 75cc for a lower comp than 10.7:1

yes! that sounds like it'll be quite the setup. :)

Thanks, I'm new in engine rebuilt and all this is good to know.